In computer networking, a Media Access Control (MAC) address is a unique identifier assigned to most network adapters or network interface cards (NICs) by the manufacturer for identification, and used in the Media Access Control protocol sublayer. If assigned by the manufacturer, a MAC address usually encodes the manufacturer's registered identification number. It may also be known as an Ethernet Hardware Address (EHA), hardware address, adapter address, or physical address.
There are three numbering spaces, managed by the Institute of Electrical and Electronics Engineers (IEEE), which are in common use for formulating a MAC address: MAC-48, EUI-48, and EUI-64. The “EUI” stands for Extended Unique Identifier.
Although intended to be a permanent and globally unique identification, it is possible to change the MAC address on most of today's hardware, an action often referred to as MAC spoofing. Unlike Internet Protocol (IP) address spoofing, where a sender spoofing their address in a request tricks the other party into sending the response elsewhere, in MAC address spoofing (which takes place only within a local area network), the response is received by the spoofing party.
In a network system wherein modules are integrated in a tandem or other integrated configuration that use at least two sets of image path boards, the image path boards do not have unique MAC addresses and therefore cannot communicate independently with the Program and Systems Information Protocol (PSIP).